Project Summary The present study focuses on our discovery that developmentally silenced SIX-family transcription factors are reactivated by TNF-family cytokines and potently suppress gene expression programs induced by non-canonical NF-kB. By first characterizing the human cytokines and pathogen associated molecular patterns (PAMPs) that induce Six1 and Six2 protein expression and by then investigating the molecular components required for their reactivation (Aim 1), these studies will reveal a new pathway for non-canonical NF-kB regulation in the mammalian immune system. Second, we will determine how Six-proteins inhibit inflammatory gene expression programs through promoter proximal mechanisms (Aim 2). Physiological significance of inflammatory resolution by Six-proteins while be investigated in mammalian model organisms using three complementary mouse models of Six1 protein function (Aim 3). Insights gleaned from these studies will explain how non-canonical NF- kB is regulated at gene promoters and will also reveal co-repressor complexes that play important roles in the inflammatory response to microbial pathogens. Developing new drugs that interfere with the ability of SIX proteins to regulate non-canonical NF-kB during microbial infection would be an innovative approach to combat human disease associated with NF-kB signaling dysfunction including chronic inflammation. Therefore, by revealing molecular details of SIX-protein function in the mammalian immune system, from biochemistry to mouse models of infection, we will uncover sites of potential weakness that may be exploited for therapeutic intervention. Importantly, these studies will also provide new insights into the pathogenic mechanisms of an important infectious disease-causing agent and also into the biology of the human inflammatory response.